The present invention pertains to valves which may be used for intake or exhaust of gases from compressors, and more specifically, to reciprocating compressors. The operative portion of such a compressor includes at least one piston and cylinder assembly, and the intake and exhaust valves are typically located at or near the cylinder head. It is known to use the same form of valve for both intake and exhaust, simply reversing the position of the valve for the two uses, respectively.
One such valve is disclosed in Assignee's prior U.S. Pat. No. 3,536,094. This valve has two annular valve elements arranged concentrically with respect to each other and to the valve as a whole, and each reciprocating between stop surfaces and valve seating surfaces formed, respectively, on opposed plates forming the valve case. Each valve element is biased closed, i.e. toward its seating surfaces by a plurality of springs circumferentially spaced thereabout. In an alternate embodiment, the two annular valve elements are integrated by interconnecting them with small radially extending webs.
In some of assignee's more recent commercial embodiments of this valve, the plate defining the seating surfaces has a plurality of tabs or flanges extending inwardly adjacent the outer diameter of each respective set of seating surfaces, and circumferentially spaced thereabout, to guide the seal rings in their reciprocatory movement.
In such prior valves, it is very preferable that the valve elements be formed of a hard plastic material, rather than metal, for reasons more fully explained in the prior patent specification.
Although Assignee's prior valves according to U.S. Pat. No. 3,536,094 continue to be highly successful, they tend to be directed primarily to specialty markets. One reason for this is that the hard plastic material of which the valve elements are formed must be of a relatively expensive, high impact, heat, and chemical resistant material, and the valve elements are of such various sizes that they must be custom made; the sizes of the valve elements must be tailored to various size valves.
There have been suggestions in the prior art to utilize a plurality of poppet-type valves, incorporated in a single valve case, for such compressor intake and exhaust. An example is described in U.S. Pat. No. 4,489,752 to Deminski.
Historically, poppet valves have only been successful in low differential pressure applications (300-400 psi) at relatively low speeds (300-400 compressor strokes/minute). The valve elements of traditional poppet valves are more or less mushroom shaped, with the head of the mushroom defining the sealing surface for engagement with the valve seat, and the stem of the mushroom being utilized for guidance of the valve element in its reciprocatory movement.
It is desirable, in these valves, to minimize pressure drop and differential pressure. High differential pressure can cause extrusion of the valve element into the seat flow holes. Achieving low pressure drop typically requires a relatively high "lift" or reciprocatory stroke of the poppet. The high lift can work with the seat flow hole diameter to provide a relatively large available flow area for the gases. Reducing the seat flow hole diameter can help to prevent such extrusion, but only at a penalty of loss of efficiency. Thus, relatively large diameter seat flow holes are typically used, and even then, they must be accompanied by a relatively high poppet lift, as reductions in lift likewise tend to decrease efficiency. In short, there is a balancing act involved in utilizing poppets for this type of application, and it has traditionally been balanced successfully only in the aforementioned low differential pressure and low speed applications.
The Deminski patent seeks to address some of these problems by reducing the overhang of the traditional mushroom form and by a special aerodynamic shape of the upper part of the poppet or valve element.
The current and apparent future trend in the compressor art toward higher operational speeds would appear to further militate against the use of poppet-type valves with such compressors.